Where does charcoal, or black carbon, in soils go?

Where does charcoal, or black carbon, in soils go?
Charred boreal forest after a fire has raged: where does the "charcoal" go? Credit: Stefan Doerr, Swansea University

(Phys.org) —Scientists have uncovered one of nature's long-kept secrets—the true fate of charcoal in the world's soils. The ability to determine the fate of charcoal is critical to knowledge of the global carbon budget, which in turn can help understand and mitigate climate change. However, until now, researchers only had scientific guesses about what happens to charcoal once it's incorporated into soil. They believed it stayed there. Surprisingly, most of these researchers were wrong.

The findings of a new study that examines the result of once it is deposited into the soil are outlined in a paper published this week in the journal Science.

The international team of researchers was led by scientists Rudolf Jaffe of Florida International University and Thorsten Dittmar of the German Max Planck Society.

"Most scientists thought charcoal was resistant," says Jaffe. "They believed that once it was incorporated into soils, it stayed there. But if that were the case, soils would be black."

Charcoal, or , is a residue generated by combustion including and the burning of fossil fuels.

When charcoal forms, it is usually deposited into the .

"From a chemical perspective, no one really thought it dissolved, but it does," Jaffe says.

"It doesn't accumulate for a long time. It's exported into wetlands and rivers, eventually making its way to the oceans."

It all started with a strange finding in the .

At the National Science Foundation (NSF) Florida Coastal Everglades Long-Term Ecological Research (LTER) site—one of 26 such NSF LTER sites in ecosystems around the world—Jaffe studied the glades' environmental chemistry.

Dissolved is known to be abundant in wetlands such as the Everglades and plays a critical role in the ecology of these systems.

Jaffe wanted to learn more about what comprised the organic carbon in the Everglades.

Where does charcoal, or black carbon, in soils go?
The familiar look of charcoal; some charcoal is generated by wildfires and burning fossil fuels. Credit: Wikimedia Commons

He and colleagues discovered that as much as 20 percent of the total dissolved organic carbon in the Everglades is charcoal.

Surprised by the finding, the researchers shifted their focus to the origin of the dissolved charcoal.

In an almost serendipitous scientific journey, Dittmar, head of the Research Group for Marine Geochemistry at the University Oldenburg in Germany, was also tracing the paths of charcoal, but from an oceanographic perspective.

To map out a more comprehensive picture, the researchers joined forces. Their conclusion is that charcoal in soils is making its way into the world's waters.

"This study affirms the power of large-scale analyses made possible through international collaborations," says Saran Twombly, program director in NSF's Division of Environmental Biology, which funded the research along with NSF's Directorate for Geosciences.

"What started out as a puzzling result from the Florida Everglades engaged scientists at other LTER sites in the U.S., and eventually expanded worldwide," says Twombly. "The result is a major contribution to our understanding of the carbon cycle."

Fire is probably an integral part of the global carbon cycle, says Dittmar, its effects seen from land to sea.

The discovery carries significant implications for bioengineering, the scientists believe.

The global carbon budget is a balancing act between sources that produce carbon and sources that remove it.

The new findings show that the amount of dissolved charcoal transported to the oceans is keeping pace with the total charcoal generated by fires annually on a global scale.

While the environmental consequences of the accumulation of black carbon in surface and ocean waters are currently unknown, Jaffe said the findings mean that greater consideration should be given to carbon sequestration techniques.

Biochar addition to soils is one such technique.

Biochar technology is based on vegetation-derived charcoal that is added to agricultural soils as a means of sequestering carbon.

As more people implement biochar technology, says Jaffe, they should take into consideration the potential dissolution of the charcoal to ensure that these techniques are environmentally friendly.

Jaffe and Dittmar agree that there are still many unknowns when it comes to the environmental fate of charcoal, and both plan to move on to the next phase of the research.

They've proved where charcoal goes.

Now they'd like to answer how that happens, and what the environmental consequences are.

The more scientists can understand the process and the environmental factors controlling it, says Jaffe, the better the chances of developing strategies for sequestration and mitigating .

Explore further

Limitations of charcoal as an effective carbon sink

More information: Paper: www.sciencemag.org/content/340/6130/345
Journal information: Science

Citation: Where does charcoal, or black carbon, in soils go? (2013, April 18) retrieved 18 October 2019 from https://phys.org/news/2013-04-charcoal-black-carbon-soils.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Apr 18, 2013
For the interested folks, see an earlier article in phys.org http://phys.org/n...sly.html

Black carbon larger cause of climate change than previously assessed

January 15, 2013

This is also paywalled, but this article has much much more discussion.

Apr 18, 2013
What's going on here? This is not the discovery of a new source of CO2 in the atmosphere, but a refinement in tracking the carbon cycle in soils and the oceans. In other words, a significant amount of carbon (not CO2) is moving from soils into the ocean. What happens to it there? It either gets oxidized into CO2 or gets sequestered on the sea bottom. Probably some of both, and how much of each may depend on the river or marsh that transferred it into the sea.

So lots of detailed work needed. The overall change in the current picture is that the oceans can absorb more carbon than expected.

Oh, and this may be a good carbon sequestration method. Play with the flow of the Mississippi and other large rivers (at their deltas) to deliver more carbon to levels where photosynthesis won't intercept it.

Apr 19, 2013
Fire is probably an integral part of the global carbon cycle, says Dittmar, its effects seen from land to sea.

This seems to make a lot of sense, given the prevalience of fire over the whole planet. Reminds me a bit of the discovery of fire's role in forest management in the late 80's and the subsequent realization that not all fires should be fought. Scientists involved in forest studies and forestry experts were unsurprised, treating the "discovery" like a "duh" moment.
The rate that the charcoal dissolves and is removed to the oceans interests me. I wonder how this may affect CO2 sequesrtration from the atmosphere.

Apr 20, 2013
Well this is a well timed acticle for me, as just this morning I was thinking of what happens to charcoal in soil. Over the years, I have burned many tree stumps in a fire pit. I empty the fire pit, and have built a mound of the fire ash/charcoal on some of my land which is very poor in quality, and little vegetation. The mound has of course weathered, and all that grows in or on it seems to be some kind of surface mould/fungus. Hence the mound has crustered over, but not much else. So my thoughts are, what is the best thing to do with this ash/charcoal, to try and improve this area of land? Can it be useful at all? Can human urine be mixed with the charcoal to improve nutrient value for any biology that may colonise it? I realise manure and aditions of soil, will help, but I'm wondering about easy ways to use this charcoal material. Should I put it into a blender to make fine particles, or leave as is, so bacteria can utilise the porosity of charcoal for a habitat?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more